The Impact of Time-Dependent WSA Boundary Conditions on Magnetic Connectivity and Mesoscale Solar Wind Structure

Time-dependent (TD) heliospheric simulations driven by evolving Wang-Sheeley-Arge (WSA) model boundary conditions are increasingly relevant for improving heliospheric solar wind modeling. In this study, we quantify the differences between TD and steady-state (SS) simulations using a 2.5D MHD model of the solar wind from 0.1 AU to 1 AU in the ecliptic plane. Simulations are performed for solar maximum (December 2013) and solar minimum (December 2018) using high-cadence WSA maps (~60 minute) as inner boundary conditions. We find that compared to SS simulations, TD runs produce mesoscale fluctuations in solar wind velocity, density, and magnetic field that span radial scales of $0.1$-$0.4$ AU and longitudinal scales of 36∘-134∘. We find that the magnetic field line connectivity at 1 AU in TD simulations differs from the ideal Parker spiral by up to 40∘ ± 25∘ during solar maximum and 10∘ ± 5∘ during solar minimum, while magnetic field line path length differences reach ~0.4 AU, leading to ~2 minute SEP arrival time errors for a synthetic 1 MeV SEP event even away from the heliospheric current sheet (HCS). We also assess the impact of WSA map update cadence on the simulated wind. We find that increasing cadence from 1 hour to 128 hours leads to magnetic connectivity errors up to ± 80∘, root-mean-square radial velocity deviations $>$50 km s⁻¹, and suppression or artificial enhancement of mesoscale fluctuation amplitudes – particularly in regions with rapid HCS evolution. Our study highlights the importance of high-cadence, time-dependent boundary conditions in modeling heliospheric solar wind structure.